1. Technical Field
This invention generally relates to power supply components for computer systems. More specifically, this invention relates to power interlock systems.
2. Background Art
The development of the EDVAC computer system of 1948 is often cited as the beginning of the computer era. Since that time, computer systems have evolved into extremely sophisticated devices, and computer systems may be found in many different settings. Modern computer systems vary in their design and architecture, with many different models available to achieve the desired combination of speed, power and efficiency for any given computing environment.
In addition, most computer systems are used for a wide variety of tasks and, therefore, need to be flexible and versatile enough to change with the varying requirements of the computer user over time. For example, as the number of computer users on a given computer network increases, additional network components such as network cards and cables/adapters may need to be added. Further, as organizational changes occur, the type and quantity of data being stored and processed may also change, requiring new or additional equipment such as external secondary storage devices.
To facilitate increased versatility for a wide range of users, many modern computers, such as the IBM AS/400, use expansion slots known as Peripheral Component Interconnect (PCI) slots. PCI slots provide an industry standard expansion card/slot interface which allows different types of PCI Input Output Adaptors (PCIIOA cards or "PCI cards") to be quickly and easily added to an existing computer system. These PCI cards can be configured with various hardware/software components and used to expand or add various features or functional capabilities to a computer (i.e., expanded memory, multi-processor capabilities, etc.). In addition, PCI cards can also be configured with adapters for various connecting cables which allow a computer to interface with a host of external peripheral devices, thereby further increasing the functionality and/or versatility of the computer system.
The types of devices which may be connected to a given computer system through the use of a PCI card/slot interface are practically limitless. Several of the most common devices which are typically connected via a PCI card/slot interface to a computer include: hard disk drive controllers; network interface cards, such as token ring adaptors, Ethernet adaptors, etc.; COM adaptors for modems, facsimile machines, etc.; and Small Computer System Interface (SCSI) Controllers for adding tape drives, CD ROM drives, etc.
To provide a wide variety of expansion capabilities, most computers will have a series of PCI slots built into the computer's chassis or frame and which are each sized and positioned to receive a PCI card. Since the PCI slots provide direct access to the internal power system of the computer, the access openings to any empty PCI slots will typically be covered by a metal PCI slot access cover or "blank" to prevent foreign objects from entering the computer's frame or chassis. To install a PCI card, the PCI slot access cover is removed from the frame and the PCI card is inserted through an opening in the chassis/frame which provides access to the PCI slot associated with that access cover. Once inserted into a PCI slot, the PCI card is typically secured in place with one or more screws. After installation, the PCI card is typically powered by the internal power system of the computer and the PCI card can communicate directly with the computer.
Since the PCI slots have connectors that provide access to the power system of the computer, inadvertent contact with an empty yet "hot" PCI slot may result in serious injury or, in the case of computers with larger power supplies, death from electrocution. In most smaller personal computers, the risk of injury is fairly remote because the power supplies are fairly low power. However with larger computer systems containing high capacity power supplies, the potential for injury is relatively significant, because the amount of power required to operate larger computer systems is much greater than most personal computers.
As a result of this potential electrocution hazard, Underwriters Laboratories (U.L.), a certification group for items such as computer systems power supplies, requires that some type of safety system be installed on larger computer systems to prevent inadvertent access to the computer's power supply through an empty PCI slot. The U.L. standards for these protective measures are outlined in U.L. standard 1950, 3.sup.rd edition, clause 2.8.
One method that has been adopted by several computer manufacturers in an effort to comply with the U.L. requirement is a power interlock system which controls the computer system's power supply. For example, on the IBM AS/400 9406 model 620, an single external plastic cage is placed over the access covers for all of the PCI slots. The plastic cage is large enough to cover all of the PCI slots on the AS/400, whether they are full or empty, and extends a slight distance out from the back of the computer frame or chassis. The cage also has a number of small holes which allow air flow but which are small enough to prevent access to the inside of the cage and, by extension, into any empty PCI slots. One end of the cage includes a single electrical connector, which, when the cage is properly installed, connects with an adaptor built into the frame of the computer. If the connector and the adaptor are not connected (i.e., the cage is removed to access the PCI slots), a power interlock system is activated and the computer system will not "power up." Alternatively, is the computer system is already powered up when the cage is removed, the combination of the cage/interlock system immediately shuts the power supply off. While very effective from a safety perspective, this is a relatively inefficient, time consuming, and unnecessary process for several reasons.
For example, it is often desirable to add or remove cables from network PCI cards to alter a network configuration. While the act of adding a cable is simple enough, the cage not only prevents access to the PCI cards, but also to the cables connected to the PCI cards. This means it is necessary to power down the entire computer system for even the most minor re-configurations. Typically, a user will shut the system down, remove the protective cage, add, remove, or otherwise reconfigure the desired cables, reinstall the protective cage and then the computer system back on line. This also means that a single bad cable can necessitate bringing the entire system down in order to replace the single defective cable. Not only is this process somewhat inconvenient, it can significantly reduce productivity since all of the users connected to the system have to wait for the system to be powered up before they can access the system and continue working.
Without a less intrusive mechanism for disabling the power supply, many computer systems will continue to be less convenient to use and certain modifications or enhancements may not be adopted due the undesirable operational inefficiencies which are associated with the present electrocution hazard preventive safety measures.